i found this on the 'net, hope it helps answer your question. sapphira

Low dose birth control pills (BCPs) like Alesse, EstraStep, and Loestrin can effectively minimize perimenopause symptoms like hot flashes, irritability, mood swings and help with sleeping troubles, for many women.

BCPs work to decrease perimenopausal symptoms by stopping or suppressing the body's monthly ovulation. This stops our ovaries from making estrogen and progesterone.

There is a whole new group of BCPs like Loestrin that were created especially for women over 35 years of age. Not only do they function to help with the often disruptive symptoms of perimenopause, they work as an effective means of birth control. They contain just enough estrogen and progesterone to prevent pregnancies and help with perimenopause.

Today's BCPs contain a lot less estrogen and progesterone than those in the 70s and 80s.

When using BCPs all the estrogen and progesterone we receive will be from the pill. This gives you a steady and stable amount of progesterone and estrogen every day- instead of the peaks and valleys that our bodies make during perimenopause. It's these peaks and valleys of estrogen and progesterone from our ovaries that cause the flashes, trouble sleeping irritability etc...

BCPs are different from HRT (hormone replacement therapy) like Prempro because the BCPs contain enough estrogen and progesterone to suppress or stop ovulation, whereas HRT does not, it works differently and is not a form of birth control.

Using BCPs to help control hot flashes, menstrual irregularities, mood swings etc... is known as suppressive therapy as opposed to HRT which is to replace hormones that are either "lost" or need to be increased.